1. Field of the Invention
The present invention relates to a rectifying device used in, for example, a DC/AC converting circuit.
2. Discussion of the Background
Attempts have been made to achieve a high-speed MOS transistor through the miniaturization of the gate length. In recent years, however, the reduction of the gate length to a submicron level has been achieved. This involves an increase in a channel field strength and a trapping of electrons and holes in the gate oxide film, presenting an operation error problem.
In order to avoid such a problem, attempts have been made to lower the power supply voltage. Conventionally, the integrated circuit using MOSFETs has been driven at a power supply voltage of 5V. However, there has emerged an integrated circuit operating at a power supply voltage of 3.5V with a gate length of 0.35 micron currently achieved. This trend is further continuing into the future and, if a gate length of below 0.2 micron is achieved, it will be necessary to lower the power supply voltage to about 2V.
For those apparatuses using such an integrated circuit or circuits it has been necessary to be equipped with a corresponding DC power supply. As such a DC power supply use is usually made of a switching regulator. However, the power loss by a rectifying device presents a problem because a power supply voltage involved is lowered.
That is, for a usual silicon pn-junction diode it is necessary to apply a voltage of the order of 0.6V at a time of conduction. With a DC power supply of 2V, however, as large as 23% loss is caused due to the diode. It is thus desirable to use a diode adapted to be turned ON at a lower voltage level. Even if a schottky diode is used, there unavoidably occurs a forward voltage drop of about 0.4V. As a result, less power efficiency results from a forward voltage drop of the diode and a serious consequence is involved.
A forward voltage drop across the diode is usually substantially proportional to the forbidden band of a semiconductor and, using a semiconductor of a narrower forbidden band width, can be lowered. The narrower forbidden band width deteriorates the backward withstand voltage and temperature characteristic, so that, usually, use is never made of any semiconductor having a narrower forbidden band width than the forbidden band width of silicon (=1.1 eV). For this reason, less power efficiency of a power supply circuit is unavoidable against an integrated circuit having a power supply voltage of about 2V in particular.
As set out above, with the conventional rectifying device, the power loss by the forward voltage drop is unavoidable and the efficiency is extremely reduced at a low power supply voltage of below about 2V in particular.